Retrieving the displacements of the Hutubi (China) underground gas storage during 2003-2020 from multi-track InSAR

Many countries and regions build underground gas storages (UGSs) to regulate the energy demand and supply in different seasons. The Hutubi underground gas storage (HUGS) in Xinjiang province is the largest UGS in China, so it is of great significance to monitor its operation. At present, the researches on the HUGS mainly rely on traditional geodetic monitoring (e.g., in-situ leveling and global navigation satellite system (GNSS)), which has a short time span and low spatial resolution. The whole-domain and long-temporal sequence surface displacements induced by gas recovery (before 2013) and injection/extraction (since 09/06/2013) were seldom reported. In this study, the large-scale background deformation was firstly obtained using the ALOS PALSAR data (2006-2011), and the displacement time series of the HUGS over 2003-2020 was observed by all available Synthetic Aperture Radar (SAR) data from multiple SAR sensors (Envisat ASAR, TerraSAR/TanDEM-X, Sentinel1). The results show that this area had a long history of slow subsidence (2.2 mm/yr) before 2013. Since 06/ 2013, the surface of the HUGS showed periodic uplift and subsidence with a net uplift. The average uplift rate in the center was about 7 mm/yr during 08/2013-07/2015 and 13 mm/yr during 03/2015-05/2020. The deformation has a temporal correspondence with the gas extraction/injection process. The accuracy is assessed by the cross-validation of the results of different datasets and the GNSS measurements. The compound dislocation model (CDM) is used to model the dynamic displacements caused by gas injection/extraction in HUGS. This model can reflect the UGS volume changes and the estimated central depth (3499.7 m) and height (108.6 m) of the storage are consistent with the actual central depth (-3585 m) and height (-110 m). We also restore the dynamic change of the pore pressure and the injected gas volume during the 5-7 cycles, on the basis of the linear relations between gas injection volume, pore pressure, and CDM parameters. In 12/2017, the estimated gas inventory of the HUGS is 91.29 x 108 m3, about 4.7% smaller than the real gas inventory of 95.77 x 108 m3. At the end of the seventh injection/extraction cycle, the predicted maximum gas injection volume and pore pressure reached 11.2 billion m3 and 36 MPa, respectively.